358 Prof. E. Claparede on the Structure of the Annelida. 



parency of the crystalline is incontestable in many cases, Miiller's 

 opinion as to the functional value of this organ must not be re- 

 jected. The eyes of the Nereides and of most of the Annelida 

 appear to be destitute of any apparatus of accommodation. If 

 therefore we assume that the perceptive elements are lodged be- 

 tween the granules of the pigment, only objects placed at a 

 determinate and perfectly fixed distance can project their images 

 upon the surface of this choroid pigment. The vision of the 

 animal would, in this case, necessarily be very restricted. This 

 difficulty disappears if we seek in the crystalline at once a re- 

 fractive body and a perceptive organ, nearly as we seem compelled 

 to admit with regard to the crystalline cones of the Arthropoda. 

 The image projected at various depths in the crystalline by 

 objects placed at variable distances would then always be formed 

 in a sensitive layer. 



Regeneration of Mutilated Parts. 



The observations of Bonnet upon the regeneration of muti- 

 lated parts in the Earthworms, confirmed by Lyonnet, Reau- 

 mur, Duges, &c., were hesitatingly doubted by Vandelius'^ 

 and Bosc f, and more recently and positively by Dr. Williams %, 

 M. Vogt (^, and others. We must therefore be thankful to 

 those who, like Dr. Baird ||, have brought to light certain early 

 observations, or, like M. de Quatrefages ^, have corroborated 

 and confirmed them by fresh experiments. 



The reproduction of mutilated parts in the Annelida is in- 

 contestable. A great number of these worms, perhaps all, can 

 even reproduce the anterior region including the head. Among 



* " Dominici Vandelii philosophi ac medici dissertationes tres. De 

 Aponi Thermis, de iiormullis insectis terrestribus, et Zoo])hytis marinis, et de 

 Verraium terra; reproductione, atque Tcenia canis. Padua, 1/58," pp. 98- 

 147. This work, which seems to have been forgotten, is nevertheless the 

 prodnction of a good observer. In very careful experiments, repeated for 

 two successive years, he did not succeed in seeing mutilated Earthworms 

 reproduce their anterior extremity. He, nevertheless, prudently con- 

 cludes that these experiments require to be made with extreme care, and 

 does not accuse Reaumur of having deceived himself. We know that 

 Duges afterwards likewise began by obtaining negative results, but that 

 subsequent experiments succeeded with him completely. The regeneration 

 of the anterior part takes ])lace, in fact, only when the number of seg- 

 ments removed is not too great. 



t Histoire Naturelle des Vers, tome i. pp, 128 & 215. 



X " Report on the British Annelides," Report of the British Association, 

 1851, p. 247. 



§ Vorlesungen iiber niitzliche und schadliche, verkannte und verlaum- 

 dete Thiere. Liepzig, 1864, p. .91. 



il Johnston's Catalogue of British non-parasitical Worms. Appendix. 



1[ Ann. Sci. Nat. tome ii. 1844, p. 100 ; Hist. Nat. des Anneles, tome i. 

 p. 126. 



